The ability of projection display apparatuses to display enlarged given images on a projection screen has led to their extensive use in presentations. In a presentation an explanation is provided based on projected images, so it is convenient to be able to overlay the images with an embellishment effect image (embellishment image) such as an arrow graphic or the like to indicate specific locations on the projected image.
In prior art projection display apparatuses, when, for example, an embellishment effect image is overlaid on an original image given from a personal computer, the embellishment effect image has been overlaid in the personal computer. Based on overlay image signals output from the personal computer, the projection display apparatus displays on the projection screen the image on which the embellishment effect image is overlaid. However, in this case, it has been necessary for a specific application program to be installed beforehand in the personal computer for performing processing based on commands from the projection display apparatus. Moreover, when signals given to the projection display apparatus are image signals output from a video recorder or television, it has not been possible to overlay an embellishment effect image on the original image. That is, a problem has been that whether or not an embellishment effect can be imparted to a projected image has depended on the capabilities of the image supply apparatus that supplies an image to the projection display apparatus.